Firearms Identification: Matching Bullets

"ForeWord" Notes

• A bullet fired from one gun will not have the same markings as a bullet fired from another gun.

"Introduction" Notes

• Cause and effect relationships involving natural laws have long been recognized by courts.
• Examples include dry grass igniting from locomotive sparks, charred substances indicating high temperature exposure, illuminating gas igniting upon contact with a flame, and ships suffering damage from hurricanes.
• The uniform operation of natural laws, when they make or mark tangible objects, helps determine the identity of a product.
• Machines inevitably develop unique defects through wear and accident, such as scars or bruises, which aids in their identification.
• Studying examples helps us understand how things can be alike, then we can determine the likelihood of things looking similar.
• This can be thought of by looking at similar puzzle pieces to find the missing puzzle piece

"Chapter 1" Notes

• Identification of firearms based on ammunition depends on solving six problems:
  • Determining the firearm type and make from a bullet (Type I).
  • Determining the firearm type and make from a fired cartridge case (Type II).
  • Determining if a bullet was fired from a suspected firearm (Type III).
  • Determining if a fired cartridge case was fired in a suspected firearm (Type IV).
  • Determining if two or more bullets were fired from the same firearm (Type V).
  • Determining if two or more fired cartridge cases were fired in the same firearm (Type VI).
• A firearm propels a projectile using the expansive force of gases from an explosive substance's combustion.
• A firearm's simplest form comprises a tube/barrel with a cylindrical bore, through which the projectile is propelled by gases.
• One end of the barrel contains a chamber for the explosive substance and projectile, along with a means for ignition.
• The muzzle is the end of the barrel where the projectile exits, while the opposite end is the breech.
• The breechblock closes the breech and prevents gas escape.
• Firearms can have multiple barrels, each with a chamber, or chambers in a rotating cylinder.
• Small arms are ordnance firearms that propel projectiles less than one inch in diameter.
• Firearm identification from ammunition primarily deals with concealable small arms.
• Substances used to propel projectiles are classified as propellants, commonly termed propellent powders, and the amount is known as the powder charge.

Types of Propellants

• Black powder is the oldest propellant, a mechanical mixture of potassium nitrate (75%), charcoal (15%), and sulfur (10%).
• It's typically made of small black grains polished with graphite.
• Brown powder has a larger percentage of potassium nitrate, a smaller percentage of sulfur, and its color results from underburned charcoal.
• Both Black and Brown powder contain inorganic substances and leave a large solid residue in the bore of a firearm after ignition.
• Smokeless powders are not completely smokeless and contain organic compounds and leave no solid residue in the bore of a firearm after the ignition of a charge.
• Two general classes of smokeless powders are nitrocellulose and nitroglycerin.
• Nitrocellulose powders are colloided masses of nitrocellulose with a volatile solvent and diphenylamine as a stabilizer.
• They usually come in cylindrical, single-perforated grains or round flakes coated with a small percentage of graphite.
• Nitroglycerin powders are mixtures of nitrocellulose with nitroglycerin, typically in cylindrical, single-perforated grains or round or square flakes.
• Ballistite is a typical nitroglycerin powder made by gelatinizing low nitrated nitrocotton with nitroglycerin.
• Cordite is a modification of ballistite which derives its name from its cord-like appearance and is a nitroglycerin-nitrocellulose powder.
• Bull's-eye powder is another nitroglycerin-nitrocellulose powder, granulated in solid cylindrical disks.
• Pistol powder No. 5 is a nitrocellulose powder.
• E. C. powder and Kynoch are mixtures of nitrocellulose with potassium and barium nitrates, leaving some solid residue in the bore due to inorganic compounds.
• Small arms have helical or spiral grooves cut into the bore's smooth surface, termed rifled barrels.

Gage and Caliber

• Gage refers to shotguns where the bore diameter equals the diameter of a lead ball whose weight in pounds is the reciprocal of the gage index.
  • A 12-gage shotgun's bore diameter is the diameter of a lead sphere weighing one-twelfth of a pound.
• Caliber indicates a firearm's bore diameter.
  • A .38 caliber revolver of a certain make has a bore diameter of 0.36 inch.

Ignition and Ammunition

• The percussion cap ignites the powder charge in muzzle-loading firearms using percussion locks.
• It’s a small metallic cup with a priming mixture, placed on a nipple at the breech end of the barrel.
• A hammer blow, released by a trigger pull, crushes the priming mixture, creating a flame communicated to the powder charge through a vent in the nipple.
• The priming mixture commonly contains fulminate of mercury.
• Three types of fixed ammunition used in small arms: pin-fire, rim-fire, and center-fire, each using different methods for priming mixture.
• Pin fire primer consists of a small cylindrical cup containing priming mixture that is placed in a cavity inside of the head of the cartridge case.
• The Primer explodes with the impact of the hammer on a thin pin which extends radially through the head of the cartridge into the primer.
• Rim fire is the placing the priming mixture in the cavity formed in the rim of the head of the cartridge case.
• The primer is crushed and exploded by a blow from the hammer on the rim or from a firing pin which is driving into the rim of the head of the cartridge case.
• Center fire has its primer is forced into a small cylindrical chamber in the head of the cartridge case and the primer is exploded by the impact of the firing pin.
• The flame then travels through vents into the powder chamber.
• An early center-fire ammunition form is called "centre-primed, metallic cartridges”.
• Metallic ammunition applies to cartridges with metallic cases normally loaded with a single bullet.
• Metallic ammunition cartridges are made in different calibers, sizes, types and weights of a bullet.
• Lead, full metal case, metal point, soft point, flat point, and hollow point bullets are a few of the bullet types which are used.
• Blank cartridges are also available in certain types, calibers, and sizes of ammunition..
• Metal case bullet jackets mainly consist of gilding metal or cupro nickel.
• The latter is an alloy of copper and nickel with a percentage of nickel that is dependent upon the hardness that is desired for the alloy.
• Cannelures: they are circumferential grooves appearing on bullets.
• They are knurled and hold lubricant, also receiving the crimp formed at the mouth of the cartridge case.
• Another method a bullet could be secured into a cartridge case is to indenting the case into the surface of the bullet at two or more points.
• The rimless cartridge case has a groove turned into the head for engaging the extractor in center-fire ammunition.
• An extractor mechanism withdraws a cartridge or fired cartridge case from the chamber.
• The ejector mechanism throws the cartridge or fired cartridge case from the firearm; some firearms use this same mechanism as both the extractor and the ejector.
• Center-fire revolver cartridges have rimmed heads, while automatic pistol cartridges usually have rimless heads, or cartridges for use in automatic (auto-loading) pistols are rimless.
• While it is possible to use rimless cartridges in certain revolvers, the ones that use smokeless powder have a groove so that it can't be pushed into the case too far as the reduced chamber would result in excessive pressure and can be dangerous.
• Sufficient variation exists in the weights of bullets from the same caliber, type, size, and make that you must consider expressing it to the nearest 0.5 grain.
• The 0.38 Smith & Wesson adn 0.38 Smith & Wesson Special calibers are examples of cartridges of different sizes of the same caliber of center-fire ammunition.
• While made to be the same bullet type, the .38 Smith and Wesson and .38 Smith and Wesson Special bullets come in separate sizes, so the 0.38 and Wesson won't fit in a revolver made to fit .38 Smith and Wesson Special.
• But the .38 Smith and Wesson Special is longer so it won't fit inside the smaller .38 Smith and Wesson's chamber.
• In the case that some revolvers have chambers made to use the same sized cartridge cases, putting a .38 Smith and Wesson Special would not allow it to turn.
• The .38 Smith and Wesson Special bullet has two grooves and is heavier than the smaller .38 Smith and Wesson bullet which has one groove.
• The .22 long and long rifle use the same sized cartridge case but the larger rifle carries more powder and a heavier projectile.
• To that effect, the same caliber cartridges has sufficient variation that you must consider expressing it to the nearest 0.5 grain.
• In center-fire ammunition, the primer can be removed, and the bullets reloaded after they are fired with home-made bullets, from stand mold, or by manufacturer purchased bullets.
• Helical grooves cut in the surface of the bore are called rifling.
• The raised helical surfaces are called the lands while the breech end are chamfered to form a forcing cone, leading to the bore.
• The purpose of the rifling is to cause the bullet to rotate about its axis of symmetry, stabilizing the bullet in flight.
• Rifling can be uniform or increasing twist.
• Uniform Twist is where where the twisting is constant throughout the bore.
• Increasing twist is applied muzzle end of the bore.
• Small arms barrels usually use uniform twists.
• Rifling can be either right or left handed and for small arms is expressed by the units of length it takes to make one complete turn.
• In a cross-section of the rifling of a barrel with six helical grooves and uniform twist, the raised portions l are lands, and the sides of the lands b and c are land shoulders.
• Land shoulders is pressure side and is called carry shoulder or driving edge of the land.

Microscope and Magnification

• To identify ammunition fired from a firearm, a microscope can be used
• The field or field of view of a microscope is what can be seen through the microscope when it is in focus
• Magnification is expressed in diameters or times linear.
• if you increase a circle 5 times bigger than it really is, the microscope has a magnification of 5x.
• the image becomes 5x bigger while the area becomes 25 times bigger than the real object.
• When examining bullets diameters of 15 to 20 are sufficient, but 30 is needed for special cases
• Tool marks can be examined under a microscope to identify which type of machining was used

Tool Mark Patterns

• Photomicrographs of cold-rolled steel show tool-mark patterns which are made by:
  • A power-driven hack saw.
  • Fine and coarse files.
  • A grinding wheel.
  • A lathe tool.
  • A milling-machine cutter.
  • A shaper tool.
• During metal-cutting, the metal in contact with the cutter is stressed, resulting in a tearing action instead of a shearing action
• Fineness/coarseness of the tear depends on metal properties, cut depth, and cutter properties.
• Tool-marks come from the tearing of the metal, not the blunting of the cutter.
• Fig. 27 is a photomicrograph (x30) of the cutting edge, 1/8 inch wide, of a tool bit made of high speed steel.
• Fig. 28 is a photomicrograph (x30) of the same tool bit after it was treated in an abusive manner in a shaper to cut a groove in a piece of cold-rolled steel to a depth of 1/16 inch.
• With firearms using fixed ammunition, soft metal parts get pressed against the bullets when fired.
• Parts can be made the same to ensure parts fit together in mass production because designers make plans and schedules.
• Class characteristics are controlled by those making the firearm before they re made.
• Accidental characteristics are from things that occur at random that happen during the manufacturing of the firearm and parts such as tool marks.
• Metal damage is caused by chemical reactions and erosion from used firearms.
• When the powder of a firearm is ignited, it creates pressure and causes fast speeds which can damage and wear down the barrel, surface and bullets grooves which help guide the projectile.
• In identifying firearms by ammunition fired from them , class and accidental features help explain the effect from cartridges fired.
• Specific features are called pertinent characteristics.
• Small arms can be divided into two groups:
  • Group 1: small arms with smooth bore barrles like shotguns and older firearms
  • Group 2: small arms with rifled barrels such as rifles carbines single shot pistols revolvers and machine guns automatic rifles some of these are uncommon
• Some combination shotguns have one or two smooth bores with a rifled barrel which depends on the cartridge fired the arms can be divided up further to :
  • sub group a small arms for center fire ammunition
  • sub group b small arms for rim fire ammunition
  • sub group c small arms for pin fire ammunition
  • sub group d small arms with firing capabilities similar to flintlocks matchlocks percussion locks and wheel locks
• firearms using both rim fire and center ammunition will be included in subgroups a and b
• To classify firearms, all relevant class characteristics are used to group firearms
• For each group classifications, they get smaller and more detailed
• The classification helps the firearm becomes recognizable

Identification

• When describing a person with specific descriptions, similar identification is use for fire arms to reduce the number of firearm matches

Importance of Mathematical Skills

• Estimating accidental features distributes across a large number of forearms is relies on math since it is impossible to identify all characteristics for every machine.
• Math and statistics are helpful to determining the likelihood of matches

Firearm Signatures

• Firearm signatures appear on bullets.
• Ammunition marks leave signatures on firearm parts that come in contact.
• For fixed ammunition, the cartridge case and the bullet has a signature.
• For a shotgun firing signatures appear on the barrel.
• Muzzle-loading also give signatures to ammunition from where they are being fired.
• Shot and buckshot are spread on the inside of a barrel.
• A signature is created by when the soft or hard surface has come in contact with a hard of soft surface.
• Different makes are connected through different parts of a firearm.
• Cartridges cases have parts that touch and interact with chambers ,firing pins extractor magazines etc.
• Rifled barrels can come into contact with the chamber and rifling barrel features, or forcing cone characteristics inside of the barrel.
• These come in contact with unique marks that help identify ammunitions fired form the barrels.
• Each conclusions is based on the analysis of an actual identity.
• See figures 36 ,37 and 38 which help with that and show other identifications
• When bullets make their way through the gun raised areas of the barrel causes the bullets to have markings
• Bullets are made to spin.
• Grooves aee made in a bullet on the way of it in barrel to make the bullet spin while being pushed though.

Dynamics of a Fired Bullet

• When the force pushing the bullet is no longer there , the distance slightly stretches.
• They get compressed sideways as it goes through the barrel
• The bullets face rough edges as they move and get pushed through.
• A bullet faces passive resistance from moving to barrel.
• To measure distance from a bullet , chronograph are helpful
• deformation bullet get undergo in pistol barrel may be divided into parts of forming of grooves on the surface of the bullet and second the accounts of walls driving edges and stria face.
• bullets from barrel depend of different size or if it has larger size it will have similar affect.
• formation grooves depends on the metal type as well as position of barrel.
• Stripping is the translantion of the barrel when it is not moving according to direction for rifling.
• If any bump comes on barrel it will cut or damage and shape and direction of movement depending on protrusions.

Barrel Making Process

• Barrel make can consist various of steps
  1. Drop forging: which has barrels that are made with pairs. from Hot rolled manganese are helpful
  2. Annealing: where barrel is heated and slowly cooled which help soften the load.
  3. Pickling use acid to help clean barrels and remove impurities.
  4. Trimming helps remove material shape barrel
  5. Inspection barrels are checked during stages
  6. Strength: strength is help from reheating and cooling barrel after being heated.
  7. To endure durability: to withstand hardness test are conducteds
  8. To necessary: straightening consist of smoothing barrel
  9. Smoothing edges comes fro burring.
  10. Milling comes from various barrels parts ending .
  11. Accuracy: center helps with center
  12. Roughly: The end turning is made the lugs
  13. Shape Smooth and drill for reaming .
  14. Help fine shape barrels : from ground of shapes
  15. Help with precision for reaming that is done to barel . 16.Helical grooves help make a twist

Cartridge Marks

• sharp edges on magazines or edges can leave marks.
• cases can shows some marks and not appear in the barrel.
• depending on cartridges the barrels carry marks of all the magazine marking and depending on the bullets.
• Primed cartridge has fired power and primer removed the fired primer will push partially
• this force help hit the breaches leaving impressions.
• indentations are not deep when cartridge is fire to its full potential.
• Marks are more complex from revolvers than automatics
• cylinders are chambers for cartridges designed for uniform bores
• Revolved from bullets need jump barrel while the powder gases escape cannot be.
• semi smokeless or black powders cannot be silenced.
• clear bullet base results from smoke less base with black can come a little residue.
• Bullet base gets from semi- fired or loaded to display any residue
• Foreign make don't display and some makers show name numbers.
• if firearm is know then help manufacturer can aid with providing shipping dates etc can only use these proper authorities

Characteristics Affecting the Fired Bullet

• Lead can removes grove but in better revolver that cut cause engraving and uniform may not caused the grooved to be disrupted by characteristics

Similarities and DIfferences

• Analyzing the comparison in the barrels both are different signatures.
• Extensive training will help skilled examiners and help with different analysis
• Smooth and bore can be examined depending on groves from rifling and barreling a bullet will help diameter can imply the cartridge size which mean.
• can find from revolvers type while studies bullet by that and and help characteristics and widths

Instruments

• Instrument precision using comparison and microscope can reveal a signature and diameter is more to a valuable investigator .

• Shotguns determine standards

• To examine fire helps cases is determined by types of gauge and paper metal.

• metallic cases that determine and stamp is not determine size of cases

• Fire arms need be fired for a long which are depend on the characteristics and the class by fired side

Important

• Fire head gets pressed by breech and helps different to different designs between blocks and plates

Additional Information

• A study can show firing with more deformance than show a lot help

Helpful Characteristics

• Characteristics that come into contact and ammunition such as ejector pins mag sizes and features are relevant
• Only a set of determined sizes that come down to a to help narrow the sets.
• test are used to compare a firearm with the condition and what's in side

Key observations after test fires:

• metallic material can be caused by partical of the bullets.
• depend on the powder that is used.
• depending on bullets, power the angle and cone and hard things, things could change depending on each shot type and it does have a little to little effect form gun.
• can vary according to to gun an and type and depend on condition of the gun signature can change per shot.
• It is prove to gun to tell signature and for different gun with feature that can be tested.
• the matching of the two are two the align is phase is determined or engraved.
• Relation signature is a firearm from is the to.
• If all are in sync than it have relation or congruent element in or it calls an incongruence.

Bullet Wounds

• Important data that need to be collect for damage bullets is to identify the unique

Key Notes for Homicide Investigation Steps:

• A bullet has an hard effect that can test is the bullet come from the surface it tough to analyze so
• Important element that if there is feature to stand by it or can be a difficult.
• groove that needs the more that same and will be focus to look that .
• Don't throw bullets away due to and investigator collect small data and information.

To consider coating that effects bullets to show it the sign and shape from bullets . Analysis to conduct conclusion take great skill in order and to have an effect test analysis ,

• Pin point hole may point where the breech and fire have came with contact of point. breech or the breach to lead the trigger

Rules of Evidence:

• Judges decide if it needs any witness opinions or to provide and aid to to guide to a decision, if too complex a trial to take place this this .
• and it gets to to to or is is to help with decision or if the the more is is they help from with the is not the only that experts to help decision is is.